Over the past several years, there has been increasing environmental concern over soil contamination. There are various well-known sources of contamination, including underground petroleum storage tanks used by gasoline service stations and the like. As a result of this increasing environmental concern, government regulations have come into force which place strict controls over such underground storage tanks and which will, over a period of years, eventually require replacement of a significant percentage of existing tanks. As part of the process of removing and replacing such underground storage tanks, a significant amount of the surrounding soil, typically in the range of 100-1000 cubic yards, must be removed and then treated to remove any contaminants which may have leaked from the tanks. Treatment of the soil, generally referred to as remediation, can be accomplished in several ways, including removing and disposing of the soil, or treatment of the soil on site. Disposal of contaminated soil is typically quite expensive and requires new soil to replace the soil which has been removed. In addition, such soil still is contaminated, and thus, the basic contamination problem is only moved to another, albeit typically more remote, location.
Many different systems are used for on-site soil treatment. Typically, many of these systems involve drilling a plurality of extended wells on the site, forcing the vaporization of the contaminants in some manner and then permitting the vaporous contaminants to escape through the wells. Two such systems are shown in U.S. Pat. No. 4,842,448 to Koerner and U.S. Pat. No. 4,982,788 to Donnelly. However, such methods are also quite expensive, often ineffective, and take an exceptionally long time to complete, typically on the order of 6 to 18 months. Also, many of these systems release the vaporous contaminants to the atmosphere, a practice which is also now becoming increasingly unsatisfactory, and in many areas is not even permitted, due to air quality restrictions. When the contaminants produced by on-site treatment systems are not released to the atmosphere, they are typically treated by a completely separate system, which adds to the expense and complexity of the overall process. In another on-site treatment approach, shown in U.S. Pat. No. 4,919,570 to Payne, the soil is removed and treated in a plurality of treatment vessels. While such a system can be effective, it is inherently limited to rather small volumes of soil, and again is typically expensive and somewhat complex to operate.
Thus, in view of the increasing emphasis on soil remediation relative to underground storage tank facilities, a significant need has developed for a system for efficiently and inexpensively removing contaminants from soil surrounding storage tanks.